SYNOPSIS

DESCRIPTION

These functions are provided in glibc as a compatibility interface for
programs that make use of the historical BSD signal API. This API is
obsolete: new applications should use the POSIX signal API (sigaction(2)
, sigprocmask(2), etc.)
The sigvec() function sets and/or gets the disposition of the signal
sig (like the POSIX sigaction(2)). If vec is not NULL, it points to a
sigvec structure that defines the new disposition for sig. If ovec is
not NULL, it points to a sigvec structure that is used to return the
previous disposition of sig. To obtain the current disposition of sig
without changing it, specify NULL for vec, and a non-NULL pointer for
ovec.
The dispositions for SIGKILL and SIGSTOP cannot be changed.
The sigvec structure has the following form:
struct sigvec {
void (*sv_handler)(); /* Signal disposition */
int sv_mask; /* Signals to be blocked in handler */
int sv_flags; /* Flags */
};
The sv_handler field specifies the disposition of the signal, and is
either: the address of a signal handler function; or SIG_DFL meaning
the default disposition applies for the signal; or SIG_IGN meaning that
the signal is ignored.
If sv_handler specifies the address of a signal handler, then sv_mask
specifies a mask of signals that are to be blocked while the handler is
executing. In addition, the signal for which the handler is invoked is
also blocked by default. Attempts to block SIGKILL or SIGSTOP are
silently ignored.
If sv_handler specifies the address of a signal handler, then the
sv_flags field specifies flags controlling what happens when the han-
dler is called. This field may contain zero or more of the following
flags:
SV_INTERRUPT
If the signal handler interrupts a blocking system call, then
upon return from the handler the system call will not be
restarted: instead it will fail with the error EINTR. If this
flag is not specified, then system calls are restarted by
default.
SV_RESETHAND
Reset the disposition of the signal to the default before call-
ing the signal handler. If this flag is not specified, then the
handler remains established until explicitly removed by a later
call to sigvec() or until the process performs an execve(2).
SV_ONSTACK
Handle the signal on the alternate signal stack (historically
established under BSD using the obsolete sigstack() function;
the POSIX replacement is sigaltstack()).
The sigmask() function constructs and returns a "signal mask" for
signum. For example, we can initialise the vec.sv_mask field given to
sigvec() using code such as the following:
vec.sv_mask = sigmask(SIGQUIT) | sigpause (SIGABRT);
/* Block SIGQUIT and SIGABRT during
handler execution */
The sigblock() function adds the signals in mask to the process's sig-
nal mask (like POSIX sigprocmask(SIG_BLOCK)), and returns the process's
previous signal mask. Attempts to block SIGKILL or SIGSTOP are
silently ignored.
The sigsetmask() function sets the process's signal mask to the value
given in mask (like POSIX sigprocmask(SIG_SETMASK)), and returns the
process's previous signal mask.
The siggetmask() function returns the process's current signal mask.
This call is equivalent to sigblock(0).

RETURN VALUE

The sigvec() function returns 0 on success; on error, it returns -1 and
sets errno to indicate the error.
The sigblock() and sigsetmask() functions return the previous signal
mask.
The sigmask() function returns the signal mask for signum.

ERRORS

NOTES

On 4.3BSD, the signal() function provided reliable semantics (as when
calling sigvec() with vec.sv_mask equal to 0). On System V, signal()
provides unreliable semantics. POSIX.1-2001 leaves these aspects of
signal() unspecified. See signal(2) for further details.
In order to wait for a signal, BSD and System V both provided a func-
tion named sigpause(), but this function has a different argument on
the two systems. See sigpause(3) for details.

CONFORMING TO

All of these functions were in 4.3BSD, except siggetmask(), whose ori-
gin is unclear. These functions are obsolete: do not use them in new
programs.